Unusual pseudogap features observed in iron-oxypnictide superconductors

Laser photoemission spectroscopy is employed to investigate the electronic structures of LaFeAsO:F and LaFePO:F [1] exhibiting $T_{c}$ = 26 and 5 K, respectively [2]. We find that the high-$T_{c}$ LaFeAsO:F exhibits a temperature-dependent pseudogap extending over $\sim $0.1 eV about the Fermi level at 250 K, whereas such a feature is absent in low-$ T_{c}$ LaFePO:F. We also find $\sim $20-meV pseudogap features and signatures of superconducting gaps both in LaFeAsO:F and LaFePO:F. We discuss possible origin of the pseudogaps through comparison with the cuprates. [1] Y. Kamihara \textit{et al.}, \textit{JACS }\textbf{128}, 10012 (2006);\textbf{ 130}, 3296 (2008). [2] Y. Ishida \textit{et al.}, arXiv:0805.2647.